In semiconductor manufacturing devices and chemical plants, various types of flowmeters and flow rate control devices have been used in order to control fluids, such as a raw material gas and an etching gas. Among them, a pressure-type flow rate control device is capable of precise flow rate control for various fluids with a relatively simple mechanism formed of a combination of a piezo-actuated control valve and a restriction part (orifice plate, critical nozzle, etc.), for example, and thus has been widely used.
In some pressure-type flow rate control devices, the flow rate is controlled using the principle that when a critical expansion condition P1/P2≥about 2 (P1: gas pressure on the upstream side of the restriction part, P2: gas pressure on the downstream side of the restriction part) is satisfied, the flow rate determined not by the downstream-side gas pressure P2 but by the upstream-side gas pressure P1. In a pressure-type flow rate control device of this type, simply by controlling the upstream pressure P1 using a pressure sensor and a control valve, the flow rate of the gas flowing on the downstream side of the restriction part can be precisely controlled.
Patent Document 1 discloses a pressure-type flow rate control device, which is the pressure-type flow rate control device described above and has an open/close valve including a built-in orifice as a restrictor (valve with a built-in orifice). In this pressure-type flow rate control device, the pressure on the orifice upstream side is controlled by the control valve, and also the gas outflow is controlled by the valve with a buiit-in orifice, making it possible to supply a gas at a controlled flow rate with high step-up and step-down characteristics.
In recent years, in the ALD (atomic layer deposition) process or ALE (atomic layer etching) process, it is desirable to supply a gas to a process chamber only for a short period of time, and thus it is desirable to utilize a pressure-type flow rate control device including a valve with a built-in orifice having the above characteristics.
With respect to the specific structure of a valve with a built-in orifice, various modes will be possible. For example, a metal diaphragm valve as described in FIG. 4 of Patent Document 2 has been conventionally used. In FIG. 4 of Patent Document 2, an orifice plate secured to a holder by laser welding is housed in a concavity formed in a valve seat body, and is sandwiched and secured between the valve seat body and the holder. The valve seat body is pressed and secured by an inner disc having a through-hole for the flow of the fluid.
However, in the case of using an orifice plate secured by welding to a holder or the like as described above (particularly in the case of using a thin orifice plate), due to the influence of welding heat, cracking may occur, or corrosion resistance may decrease.